1. Field of the Invention
The invention relates to a fuel cell system that includes a fuel cell and a secondary cell, and to a control method for the fuel cell system.
2. Description of the Related Art
In recent years, hybrid systems that have a secondary electric cell separately from a main energy source are drawing attention. In conjunction with such a hybrid system, there is known a construction that performs a voltage feedback control that uses a deviation between a detected voltage and a target voltage along an electric power line (see, e.g., Japanese Patent Application Publication No. 2008-29050 (JP-A-2008-29050)).
The foregoing hybrid systems include a fuel cell system that uses a fuel cell. The fuel cell system performs an intermittent operation in which the electricity generation of the fuel cell is temporarily stopped during low-load operations, such as during an idling operation, during a low-speed travel, during regenerative braking, etc., and the secondary cell is caused to supply electric power to a load (a vehicle electric motor, or the like), in order to improve fuel economy. Incidentally, during the intermittent operation, forced electricity generation is sometimes performed in order to increase the endurance of the fuel cell.
However, in the case where a related-art technology of performing the voltage feedback control is adopted in the fuel cell system, there is possibility of failing to perform a proper electric power control and therefore causing overcharge of the secondary cell during an intermittent operation of the fuel cell.